This invention relates to cleaning material from a support surface, and more particularly, it relates to an apparatus and method for removing liquid developer from a photoconductive or other surface.
In the development of electrostatic latent images where liquid developers are used to develop the image on the reusable photoconductor surface or on a reusable interposition surface, liquid developer remains on the surface after the developer image is transferred to a substrate. In these processes and apparatuses where the surface is reused to develop subsequent images, the residual liquid developer must be removed therefrom to such an extent that the residual developer will not interfere with subsequent imaging causing streaks and other image or non-image patterns and smudges of developer which transfer to subsequent substrates. In order to accomplish sufficient removal of the residual developer so that streaking and smudging of subsequent prints is eliminated, several prior art methods have been attempted, but they have resulted in failure. Wiper blades are commonly used to remove the residual liquid developers from these and other support surfaces.
U.S. Pat. No. 3,660,863 issued to Gerbasi on May 9, 1972, discloses a scraper blade acting on a xerographic drum for removing particulate toner material from the drum. In Gerbasi, the cutting edge of the blade, that is, the edge of the blade formed by the upper face surface or top surface and the front side surface, is positioned slightly below the horizontal center line of the drum and the cutting edge is held in a manner to readily cut or chisel the particulate toner material from the drum surface. This configuration is suitable for particulate toner material, however, when used for cleaning liquid developers from a support surface, problems are encountered in disposing of the liquid cleaned from the surface when the relative motion between the blade and the surface ceases. The liquid passes between the blade and surface at zero relative speeds. This leaves developer on the cleaned support surface which prints out when operation of the machine is resumed.
Blade cleaning is also described by Royka et al, in U.S. Pat. No. 3,552,850 wherein at least one self-adjusting flexible cleaning blade for pressure contact cleaning of the imaging surface is shown. In Royka et al, the leading edge of at least one cleaning blade is preferably positioned to form an acute angle of less than about 90.degree. and greater than about 20.degree. with the confronting portion of the imaging surface or plane tangent to the imaging surface at the line of blade contact to clean particulate toner from photoconductive members when means to supply a dry solid lubricant to the imaging surface are provided. This cleaning technique which is primarily a wiping action, is operable for particulate toner, but when liquid developers are used, streaking of the support surface with developer due to the interference of the intimate contact between the wiper blades and the support surface from debris, remains a problem. Furthermore, the wiping action does not suitably remove the liquid developers from the surface. Difficulties are also encountered with cleaning systems of this type using a blade which engages the surface to be cleaned when the relative motion between the blade and the surface ceases. Although the blade acts to clean substantially all the material from the surface while there is relative motion between them above a given value, it has been found that liquids will pass between the blade and the surface, possibly by capillary action at small or zero relative speeds. Furthermore if the blade is removed from engagement with the surface, a bead of liquid which has piled up against the table will spread out beyond the blade position when the blade is removed.
Thus, the liquid material will spread on the surface over a small region immediately downstream of the blade, and if the surface passes to further processing stations when the relative motion is resumed, the remaining developer material will not be cleaned off by the blades and will contaminate those further stations.
In accordance with the present invention, cleaning blades may be designated as scraper blades or wiper blades. A scraper blade is defined as one wherein the stem extends towards the tip in the upstream direction of the drum's movement and when pressed against the drum exerts a chiselling action on the material (liquid developer and debris) on the drum surface.
A blade which in operation is pressed against a support surface so that it is bent along its length in the downstream direction of the drum motion has a wiping action as it tends to be lifted up by material moving with the drum surface. A wiper blade is defined in accordance with the present invention as one in which the stem extends in the downstream direction of the drum motion. As used herein, upstream and downstream refer to drum motion.